Energy firms Npower and Scottish Power have announced more bad news for households with steep increases in gas and electricity prices.

Npower, which is based in Worecester, said prices for gas customers would increase by an average 26 per cent, with prices for electricity customers up by 14 per cent, both with immediate effect.

Scottish Power announced it would increase gas prices by an average 34 per cent and electricity prices by nine per cent from Monday.

The firms have 11.8 million customers between them. Both blamed the soaring wholesale costs, saying they had made current pricing levels unsustainable.

They are the last of the country’s suppliers to hit households with increases in recent weeks, following moves by British Gas, EDF, E.On and Scottish & Southern Energy.

Npower said the average gas customer would see an average annual increase of £162 with electricity bills rising by an average £60.

The firm claimed that until now its domestic gas prices had been the same as they were 18 months ago following a price decrease in 2007 and an increase in January, but wholesale costs had doubled.

Electricity generation had also been directly affected by the soaring price of raw materials prices, which had increased by 122 per cent for gas and coal and 79 per cent for oil over the last 12 months.

Npower managing director Giuseppe Di Vita said: “I’m sorry we’ve had to increase our prices, and we’ve made this decision extremely reluctantly, especially as household budgets are being squeezed so much at the moment.

“There is help available for people who can’t afford to pay their bills and we want our customers to get in touch if they’re worried.”